Recently, attention has been given to various oligosaccharides add efforts are being made to develop their use. Trehalose is a disaccharide widely distributed in animals, plants and microorganisms. It is proposed that trehalose be utilized as sweetening agents (Published Unexamined Japanese Patent Application No. 240758/1988), and agents for protecting proteins from drying (Published Unexamined Japanese Patent Application No. 50:0562/1988).
It is known that there are extraction methods, which make use of the natural sources of trehalose listed above. There are also microbiological fermentation methods, which make use of yeasts, Arthrobacter, Nocardia or the like. The known methods in the prior art, however, are minimally productive and not industrially feasible because they require complicated operations in the separation and purification of the desired saccharide products.
An enzymic method, in which trehalose is produced from maltose via .beta.-glucose 1-phosphate, is disclosed in Japanese Patent Publication No. 60998/1988. This method, however, has disadvantages in view of the cost of maltose as well as the cost and availability of maltose phosphorylase. In addition, trehalose phosphorylase, which catalyzes the formation of trehalose from .beta.-glucose 1-phosphate and glucose, lacks stability. Further, Euglena (green algae), the source of the trehalose phosphorylase, is not easy to culture.
Another enzymic method, in which trehalose is produced from .alpha.-glucose 1-phosphate and glucose around pH 7 in the presence of a trehalose phosphorylase obtained from Flammulina velutipes, is disclosed in FEMS Microbiology Letters, 55, 147-150 (1988). The trehalose phosphorylase from Flammulina velutipes, however, lacks stability, making its preparation rather difficult. The enzyme cannot sustain its activity at the temperature range necessary for industrial operations for an extended period of time. It therefore is concluded that the trehalose phosphorylase from Flammulina velutipes is not applicable to industrial use.
In short, although fermentation and enzymic methods are known in the prior art for producing trehalose besides extraction methods, the fermentation methods suffer from low productivity and complex isolation and purification of the end products, whereas the enzymic methods suffer from the high price of the substrate as well as the high price and poor stability of the enzyme. Thus, no industrial production of trehalose has heretofore been accomplished. It is desired to develop a process for producing trehalose by use of inexpensive substrates and enzymes of high productivity, ready availability and high stability, via an enzymic method wherein it is easier to isolate and purify the end product than in the fermentation methods.